Per the Journal of Infectious Diseases, "All viruses mutate, but influenza remains highly unusual among infectious diseases" because it mutates very rapidly, and thus, "new vaccines are needed almost every year" to protect against it. In contrast, a molecular biology journal documents that once a quality vaccine for C-19 is developed, it "would not need regular updates, unlike seasonal influenza vaccines" since the C-19 virus "does not mutate rapidly for an RNA virus because, unusually for this category, it has a proof-reading function" in its genetics. Likewise, a study published in October 2021 by The Lancet found that the "reduction in vaccine effectiveness against SARS-CoV-2 infections over time is probably primarily due to waning immunity with time rather than the delta variant escaping vaccine protection." Numerous studies have found no such waning with naturally acquired immunity.